The diversity of cell types within the vertebrate nervous system depends on patterning events that occur at early stages of development. The specification and patterning of neural tissue is closely coupled to the development of the other germ layers. The mesoderm and endoderm are important sources of signals that induce neural tissue and establish asymmetries within the neural plate. In this proposal, we seek to utilize the potent genetic and cellular methodologies available in the zebrafish to study patterning of the neural ectoderm. The zebrafish is well suited to this analysis. Zebrafish embryos are transparent and embryonic development occurs rapidly. These attributes foster detailed observation of normal and aberrant embryonic development. Zebrafish produce large numbers of offspring, which in addition to facilitating phenotypic characterization, enhances genetic analysis. The proposed experiments utilize several well characterized zebrafish mutations to investigate the molecular mechanisms that induce and pattern neural tissue. The general approach is to account for all the signals that generate anterior and posterior neural tissue. Models for both neural induction and patterning will be tested. A genetic screen is proposed to identify novel loci that disrupt anterior neural specification. The screen takes advantage of the ability to generate haploid zebrafish embryos in order to increases the throughput of the screen. There are two components to the screen: a morphology based approach to identify enhancers of a mutation (bozozok) which disrupts anterior neural patterning and an in situ based effort to detect alterations of the expression domains of the phox2a transcription factor. One promising mutation identified in a pilot screen alters anterior neural patterning and will be studied in detail. Because all vertebrates share fundamental similarities in the organization of their nervous systems, understanding the genetic networks that govern neural patterning in zebrafish will provide important insights into development of other species, including humans. Several zebrafish mutations have that disrupt embryonic development have anterior neural defects similar to a common human congenital abnormality, holoprosencephaly, and share similar etiologies. Deciphering the mechanisms of vertebrate axis formation may also provide insight into the causes other human developmental disorders.